Children's Book at the Tip of My Tongue

I remember there was a children's book where the main character is a girl who develops a disease due to not being herself, with it going away once she eats a food she had pretended to hate due to peer pressure.

I've recently remembered its existence and would like to get it for the younger kids in my family, but I cannot remember the name. If anyone could please tell me if they remember such a book, I would be infinitely grateful.

Pic unrelated.